MONTPELIER — In the penultimate debate of what has become a combative Democratic primary for attorney general, incumbent William Sorrell on Tuesday accused challenger TJ Donovan of trying to suppress turnout in the Aug. 28 vote.

During a 90-minute back-and-forth in which the candidates got to ask each other the questions, Sorrell disclosed a previously unreported incident in which the Donovan campaign asked the Vermont Democratic Party to cancel a get-out-the-vote effort scheduled to begin the day before the primary.

In an Aug. 14 email to Democratic insiders, Julia Barnes, executive director of the state party, unveiled the get-out-the-vote program. The initiative was to target a “universe” of likely Democratic voters who, based on party data, “vote sporadically” in primary elections.

Barnes said the 29,000 to 32,000 voters who would be targeted in the phone bank operation wouldn’t include individuals who had been identified as likely supporters by either the Sorrell or Donovan campaigns.

“By reaching out to these voters, the VDP will build a base of voters that are engaged in this election cycle and show our force coming out of the primary elections,” Barnes wrote.

But in an Aug. 20 correspondence to the Sorrell campaign, Barnes said the effort had been canceled “due to objections from one of the primary campaigns.”

“Let me make this clear: It was not the Sorrell campaign that said, ‘Please, don’t,’” Sorrell said in a debate hosted by the Burlington Free Press. “So my assumption is it was the Donovan campaign that objected to the Vermont Democratic Party … making this effort to enhance voter participation.”

Donovan acknowledged requesting the cancellation. Initially, Donovan said his campaign wanted to go up against Sorrell’s campaign “one on one.”

“This is going to come down to our respective abilities to turn out voters. We want to compete with you, Bill, and your team, one on one,” Donovan said. “Our primary is going to come down to people who come out. … We think we have better field organization than Bill Sorrell.”

Eric Davis, professor emeritus of political science at Middlebury College, said the Donovan campaign has good reason to oppose any get-out-the-vote effort that might neutralize his campaign’s advantage in field organization.

Generally speaking, Davis said, the advantage in low-turnout primaries goes to the candidate with the best system of voter outreach.

“It’s quite clear that Donovan’s organization is better than Sorrell’s organization. He has more endorsements, he’s raised more money, has done better field work,” Davis said. “So the conventional wisdom would say that the Donovan campaign would like to see turnout to be made up of mostly core voters.”

By enticing “sporadic” primary voters to come to the polls, according to Davis, the Vermont Democratic Party could tip the scales back in Sorrell’s favor. Given the nearly $200,000 mass-media campaign launched by a pro-Sorrell super PAC in recent weeks, Davis said, Donovan has added reason to oppose a party-sponsored get-out-the-vote program.

“All the research I’m familiar with says that kind of advertising campaign tends to work on the more casual voters rather than the core voters,” Davis said. “So it doesn’t surprise me if the Donovan campaign is less than enthusiastic about getting more casual voters to the primary, because those may be the same people who are affected by all this (pro-Sorrell) advertising.”

Sorrell used the incident to try to paint Donovan as an enemy of participatory democracy.

“The more voters the better for democracy in this state. The more voters the better for the Democratic Party in this state,” Sorrell said. “And the last thing my campaign is going to do is ask the Democratic Party (not to call) would-be Democratic voters and try to get them to vote.”

Donovan later said he opposed the effort because it was “confusing” and wouldn’t actually result in improving voter turnout.

The scrape reflected the combative tone of a debate that featured everything from unsubstantiated allegations of election fraud (made by Sorrell) to claims of illegal coordination by the Sorrell campaign with an outside political action committee (leveled by Donovan).

Sorrell said he’d been approached by Shelburne Town Clerk Colleen Haag last weekend about multiple instances in which the Donovan campaign had filled out absentee ballot forms on behalf of registered voters who never authorized it.

Donovan apologized last month for a similar incident in Brattleboro, where one of his campaign staffers requested absentee ballots for a couple who say they never asked for them.

“We got the sense (last month) that this was an isolated incident, sort of a one-time incident, right?” Sorrell said. “The Shelburne town clerk came up to me at a farmers market Saturday and was really incensed about early ballot requests from your campaign. It appears the Brattleboro incident isn’t one isolated example. There’s evidence of some widespread pattern of requesting early ballots on behalf of those who didn’t in fact authorize it.”

Donovan said his campaign has run an “aggressive grassroots operation” that involves requesting absentee ballots for likely supporters. He said it would be counterproductive for his campaign to request ballots for people who had no intention of voting for him.

He said if Sorrell has an issue, then he should submit a formal complaint to his own attorney general’s office. Contacted Tuesday afternoon, Assistant Attorney General Susanne Young, who handles elections law complaints, said her office had received no absentee ballot-related complaints.

As for throwing around allegations of illegal campaign activity, Donovan said, “If you want to go down this road, I’m glad to do it.”

Donovan said he’s heard allegations from unnamed sources about coordination between Sorrell and the super PAC funding the six-figure ad campaign on his behalf. State and federal elections law prohibits candidates from communicating with political action committees making independent expenditures on behalf of a candidate.

“I’ve heard from many people in this state who are concerned about alleged coordination between (the super PAC) and your campaign,” Donovan said.

The federal PAC, called the Committee for Justice and Fairness, is said to be funded largely by the Democratic Attorneys General Association. However, a loophole in Vermont law will allow it to avoid identifying its contributors until after the Aug. 28 primary.

“If the attorney general wants to muddy this campaign by bringing in hearsay … about people who have been aggrieved by being sent absentee ballots, then a number of people have raised issues with me about alleged coordination, which is an egregious violation,” Donovan said.

The candidates will square off in a final debate Thursday on Vermont Public Radio at noon.